Methods and apparatus for holding a substrate in a pressure chamber

ABSTRACT

A process chamber assembly for use with a substrate includes a vessel and a substrate holder. The vessel defines a chamber. The substrate holder has a rotational axis and includes front and rear opposed surfaces. The front surface is adapted to support the substrate. At least one impeller vane extends rearwardly from the rear surface and radially with respect to the rotational axis. The impeller vane is operative to generate a pressure differential tending to hold the substrate to the substrate holder when the substrate holder is rotated about the rotational axis. Preferably, the process chamber assembly includes a plurality of the impeller vanes extending rearwardly from the rear surface and radially with respect to the rotational axis.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for holding asubstrate in a pressure chamber.

BACKGROUND OF THE INVENTION

Integrated circuits (ICs), optoelectronic devices, micromechanicaldevices and other precision fabrications are commonly formed using thinfilms applied to substrates. As part of the fabrication process, it isoften necessary to remove or clean a portion or all of the thin filmfrom the substrate. For example, in the manufacture of semiconductorwafers including ICs, a thin photoresist layer may be applied to thesemiconductor substrate and subsequently removed.

Contaminants removed from surface features of microelectronic substratesafter various manufacturing steps (e.g., after post-ion implant, ‘backend of the line’ (BEOL) cleans, ‘front end of the line’ (FEOL) cleans,and post chemical mechanical planarization (CMP) steps) vary in natureand composition dramatically. Accordingly, cleaning and treating stepsmust address these contaminants with the appropriate chemistries andsolvents to either react with, ionize, dissolve, swell, disperse,emulsify, or vaporize them from the substrate. As such, a variety ofwater and solvent-based systems, and dry cleaning processes have beendeveloped to address the broad variety of waste materials.

SUMMARY OF THE INVENTION

According to method embodiments of the present invention, a method forcleaning a microelectronic substrate includes placing the substrate in apressure chamber. A process fluid including dense phase CO₂ iscirculated through the chamber such that the process fluid contacts thesubstrate. The phase of the CO₂ is cyclically modulated during at leasta portion of the step of circulating the process fluid.

According to further method embodiments of the present invention, amethod for cleaning a microelectronic substrate includes placing thesubstrate in a pressure chamber. A process fluid including dense phaseCO₂ is sprayed onto the substrate in a chamber. The phase of the CO₂ iscyclically modulated during at least a portion of the step of sprayingthe process fluid.

According to further method embodiments of the present invention, amethod for cleaning a microelectronic substrate includes providing thesubstrate in a pressure chamber containing a process fluid includingdense phase CO₂ such that the substrate is exposed to the CO₂. The phaseof the CO₂ is cyclically modulated by alternating CO₂ mass flow betweena supply of CO₂ and the chamber and between the chamber and a lowpressure source. The supply of CO₂ is at a higher pressure than thechamber and the low pressure source is at a lower pressure than thechamber.

According to further method embodiments of the present invention, amethod for cleaning a microelectronic substrate includes placing thesubstrate in a pressure chamber. A process fluid including dense phaseCO₂ is introduced into the chamber such that the process fluid contactsthe substrate to thereby clean the substrate. A portion of the processfluid is removed from the chamber. The portion of the process fluid isre-introduced into the chamber.

According to further method embodiments of the present invention, amethod for cleaning a microelectronic substrate includes placing thesubstrate in a pressure chamber. A process fluid including dense phaseCO₂ is introduced into the chamber such that the process fluid contactsthe substrate to thereby clean the substrate. A portion of the processfluid is removed from the chamber. The portion of the process fluidremoved from the chamber is distilled to separate CO₂ from othercomponents of the process fluid. The separated CO₂ is re-introduced intothe chamber.

According to further method embodiments of the present invention, amethod for cleaning a microelectronic substrate includes cleaning asubstrate in a process chamber using a process fluid including CO₂. Theused process fluid is removed from the process chamber. CO₂ is separatedfrom the used process fluid. The separated CO₂ is reused in the processchamber or a further process chamber.

According to embodiments of the present invention, an apparatus forcleaning a microelectronic substrate includes a pressure chamber andmeans for circulating a process fluid including dense phase CO₂ throughthe chamber such that the process fluid contacts the substrate. Theapparatus further includes means for modulating the phase of the CO₂while the process fluid is being circulated.

According to further embodiments of the present invention, an apparatusfor cleaning a microelectronic substrate using a process fluid includingdense phase CO₂ includes a pressure chamber. A spray member is operativeto spray the process fluid onto the substrate in the chamber. Theapparatus further includes means for cyclically modulating the phase ofthe CO₂.

According to embodiments of the present invention, an apparatus forcleaning a microelectronic substrate includes a pressure chambercontaining a process fluid including dense phase CO₂. A supply of CO₂ isfluidly connectable to the chamber. The supply of CO₂ is at a higherpressure than the chamber. A low pressure source is fluidly connectableto the chamber. The low pressure source is at a lower pressure than thechamber. Fluid control devices are operable to cyclically modulate thephase of the CO₂ in the chamber by alternating CO₂ mass flow between thesupply of CO₂ and the chamber and between the chamber and the lowpressure source.

According to embodiments of the present invention, an apparatus forcleaning a microelectronic substrate includes a pressure chamber and asupply of a process fluid including dense phase CO₂ fluidly connected tothe chamber. A distilling system includes a still fluidly connected tothe chamber and operative to separate CO₂ from the process fluid. Thedistilling system is operative to reintroduce the separated CO₂ into thechamber or a further chamber.

According to embodiments of the present invention, an apparatus forcleaning a microelectronic substrate includes a process chambercontaining a process fluid including CO₂ and means for removing usedprocess fluid from the process chamber. The apparatus further includesmeans for separating CO₂ from the used process fluid and means forreturning the separated CO₂ to the process chamber or a further processchamber for subsequent use.

According to embodiments of the present invention, a process chamberassembly for use with a substrate includes a vessel and a substrateholder. The vessel defines a chamber. The substrate holder has arotational axis and includes front and rear opposed surfaces. The frontsurface is adapted to support the substrate. At least one impeller vaneextends rearwardly from the rear surface and radially with respect tothe rotational axis. The impeller vane is operative to generate apressure differential tending to hold the substrate to the substrateholder when the substrate holder is rotated about the rotational axis.Preferably, the process chamber assembly includes a plurality of theimpeller vanes extending rearwardly from the rear surface and radiallywith respect to the rotational axis.

According to further embodiments of the present invention, a substrateholder for use with a substrate has a rotational axis and furtherincludes front and rear opposed surfaces. The front surface is adaptedto support the substrate. At least one impeller vane extends rearwardlyfrom the rear surface and radially with respect to the rotational axis.The impeller vane is operative to generate a pressure differentialtending to hold the substrate to the substrate holder when the substrateholder is rotated about the rotational axis. Preferably, the substrateholder includes a plurality of the impeller vanes extending rearwardlyfrom the rear surface and radially with respect to the rotational axis.

According to method embodiments of the present invention, a method forrotating a substrate holder about a rotational axis includes providing asubstrate holder. The substrate holder includes front and rear opposedsurfaces. The front surface is adapted to support the substrate. Atleast one impeller vane extends rearwardly from the rear surface andradially with respect to the rotational axis. The substrate holder isrotated about the rotational axis such that the impeller vane generatesa pressure differential tending to hold the substrate to the substrateholder.

According to embodiments of the present invention, a pressure chamberassembly for use with a substrate includes a vessel and a substrateholder assembly. The vessel defines a pressure chamber. The substrateholder assembly includes a substrate holder disposed in the pressurechamber, the substrate holder including a front surface adapted tosupport the substrate, and a housing defining a secondary chamber. Atleast one connecting passage provides fluid communication between thefront surface of the substrate holder and the secondary chamber. Theconnecting passage is adapted to be covered by the substrate when thesubstrate is mounted on the front surface of the substrate holder. Apassive low pressure source is fluidly connected to the secondarychamber.

According to further embodiments of the present invention, a pressurechamber assembly for use with a substrate includes a vessel and asubstrate holder assembly. The vessel defines a pressure chamber. Thesubstrate holder assembly includes a substrate holder disposed in thepressure chamber, the substrate holder including a front surface adaptedto support the substrate, and a housing defining a secondary chamber. Arestrictive passage provides fluid communication between the pressurechamber and the secondary chamber. At least one connecting passageprovides fluid communication between the front surface of the substrateholder and the secondary chamber. The connecting passage is adapted tobe covered by the substrate when the substrate is mounted on the frontsurface of the substrate holder. A low pressure source is fluidlyconnected to the secondary chamber.

According to method embodiments of the present invention, a method forholding a substrate to a substrate holder in a pressure chamber includesproviding a first pressure in the pressure chamber. A substrate holderassembly is provided including a substrate holder disposed in thepressure chamber, the substrate holder including a front surface adaptedto support the substrate, and a housing defining a secondary chamber. Atleast one connecting passage provides fluid communication between thefront surface of the substrate holder and the secondary chamber. Thesubstrate is mounted on the substrate holder such that the substratecovers the connecting passage. A second pressure is provided in thesecondary chamber that is lower than the first pressure using a passivelow pressure source.

According to further method embodiments of the present invention, amethod for holding a substrate to a substrate holder in a pressurechamber includes providing a first pressure in the pressure chamber. Asubstrate holder assembly is provided including a substrate holderdisposed in the pressure chamber, the substrate holder including a frontsurface adapted to support the substrate, and a housing defining asecondary chamber. A restrictive passage provides fluid communicationbetween the pressure chamber and the secondary chamber. At least oneconnecting passage provides fluid communication between the frontsurface of the substrate holder and the secondary chamber. The substrateis mounted on the substrate holder such that the substrate covers theconnecting passage. A second pressure is provided in the secondarychamber that is lower than the first pressure.

According to embodiments of the present invention, a pressure chamberassembly for retaining a fluid includes first and second relativelyseparable casings defining an enclosed chamber and a fluid leak pathextending from the chamber to an exterior region. An inner seal memberis disposed along the leak path to restrict flow of fluid from thechamber to the exterior region. An outer seal member is disposed alongthe leak path between the inner seal member and the exterior region torestrict flow of fluid from the chamber to the exterior region. Theinner seal member is a cup seal.

According to further embodiments of the present invention, a pressurechamber assembly for retaining a fluid includes first and secondrelatively separable casings defining an enclosed chamber and a fluidleak path extending from the chamber to an exterior region. An innerseal member is disposed along the leak path to restrict flow of fluidfrom the chamber to the exterior region. An outer seal member isdisposed along the leak path between the inner seal member and theexterior region to restrict flow of fluid from the chamber to theexterior region. The inner seal member is a cup seal. The inner sealmember is adapted to restrict flow of fluid from the chamber to theexterior region when a pressure in the chamber exceeds a pressure of theexterior region. The outer seal member is adapted to restrict flow offluid from the exterior region to the chamber when a pressure in thechamber is less than a pressure of the exterior region.

According to embodiments of the present invention, a pressure chamberassembly for processing a substrate includes a pressure vessel definingan enclosed pressure chamber. A substrate holder is disposed in thepressure chamber and is adapted to hold the substrate. A drive assemblyis operable to move the substrate holder. The drive assembly includes afirst drive member connected to the substrate holder for movementtherewith relative to the pressure vessel and a second drive memberfluidly isolated from the first drive member and the pressure chamber. Adrive unit is operable to move the second drive member. The drive unitis fluidly isolated from the first drive member and the pressurechamber. The second drive member is non-mechanically coupled to thefirst drive member such that the drive unit can move the substrateholder via the first and second drive members.

According to further embodiments of the present invention, a pressurechamber assembly for processing a substrate includes a pressure vesseldefining an enclosed pressure chamber. A substrate holder is disposed inthe pressure chamber and is adapted to hold the substrate. A magneticdrive assembly is operable to move the substrate holder relative to thepressure vessel.

According to further embodiments of the present invention, a pressurechamber assembly for processing a substrate includes a pressure vesseldefining an enclosed pressure chamber and an exterior opening in fluidcommunication with the pressure chamber. A substrate holder is disposedin the pressure chamber and is adapted to hold the substrate. A driveassembly is operable to move the substrate holder relative to thepressure vessel, the drive assembly including a housing covering theexterior opening of the pressure chamber so as to seal the exterioropening.

According to embodiments of the present invention, a pressure chamberassembly includes a pressure vessel and a guard heater assembly. Thepressure vessel defines an enclosed chamber. The guard heater assemblyincludes a guard heater disposed in the chamber and interposed between asurrounding portion of the pressure vessel and a holding volume. Theguard heater is adapted to control a temperature of the holding volume.The guard heater is insulated from the surrounding portion of thepressure vessel.

According to some embodiments of the present invention, the guard heaterand the surrounding portion of the pressure vessel define an insulatinggap therebetween. Preferably, the insulating gap has a width of at least0.1 mm.

According to some embodiments of the present invention, the guard heaterassembly includes a layer of insulating material disposed between theguard heater and the surrounding portion of the pressure vessel.Preferably, the layer of insulating material has a thickness of at least0.1 mm.

The guard heater assembly may further include a second guard heaterdisposed in the chamber and interposed between a second surroundingportion of the pressure vessel and the holding volume. The second guardheater is adapted to control the temperature of the holding volume. Thesecond guard heater is insulated from the second surrounding portion ofthe pressure vessel.

A fluid spray bar may be mounted in the guard heater. A substrate holdermay be disposed in the holding volume.

According to embodiments of the present invention, a process chamberassembly for use with a substrate and a flow of process fluid includes avessel and a spray member. The vessel defines a chamber. The spraymember includes at least one spray port formed therein adapted todistribute the flow of process fluid onto the substrate in the chamber.The spray member is operative to rotate about a rotational axis relativeto the vessel responsive to a flow of the process fluid out of the spraymember through the at least one spray port.

The spray member may include a distribution portion including adistribution channel therein, the at least one spray port extending fromthe distribution channel to exteriorly of the spray member.

The at least one spray port may extend at an angle with respect to therotational axis. Preferably, the at least one spray port extends at anangle of between about 5 and 85 degrees with respect to the rotationalaxis.

The process chamber assembly may include a plurality of the spray portsformed in the spray member.

A bearing may be interposed between the spray member and the vessel toallow relative rotation between the spray member and the vessel.

According to further embodiments of the present invention, a spraymember for distributing a flow of process fluid onto a substrateincludes a spray member including at least one spray port formed thereinadapted to distribute the flow of process fluid onto the substrate inthe chamber. The spray member is operative to rotate about a rotationalaxis responsive to a flow of the process fluid out of the spray memberthrough the at least one spray port.

The spray member may include a distribution channel therein, the atleast one spray port extending from the distribution channel toexteriorly of the spray member.

The at least one spray port may extend at an angle with respect to therotational axis. Preferably, the at least one spray port extends at anangle of between about 5 and 85 degrees with respect to the rotationalaxis.

The spray member may include a plurality of the spray ports formed inthe spray member.

The spray member may include a bar-shaped distribution portion, the atleast one spray port being formed in the distribution portion.Alternatively, the spray member may include a disk-shaped distributionportion, the at least one spray port being formed in the distributionportion.

According to method embodiments of the present invention, a method ofapplying a process fluid to a substrate includes placing the substratein a chamber of a vessel. A spray member is provided including at leastone spray port formed therein. The process fluid is distributed from theat least one spray port onto the substrate. The spray member is rotatedabout a rotational axis relative to the vessel by flowing the processfluid out of the spray member through the at least one spray port.

Objects of the present invention will be appreciated by those ofordinary skill in the art from a reading of the figures and the detaileddescription of the preferred embodiments that follow, such descriptionbeing merely illustrative of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus according to embodiments ofthe present invention;

FIG. 2 is a block diagram of a chemistry supply/conditioning systemforming a part of the apparatus of FIG. 1;

FIG. 3 is a block diagram of an alternative chemistrysupply/conditioning system forming a part of the apparatus of FIG. 1;

FIG. 4 is a block diagram of a further alternative chemistrysupply/conditioning system forming a part of the apparatus of FIG. 1;

FIG. 5 is a block diagram of an alternative recirculation system forminga part of the apparatus of FIG. 1;

FIG. 6 is a block diagram of a further alternative recirculation systemforming a part of the apparatus of FIG. 1;

FIG. 7 is a block diagram of a supply/recovery system according toembodiments of the present invention;

FIG. 8 is a cross-sectional view of a pressure chamber assemblyaccording to embodiments of the present invention in a closed position;

FIG. 9 is a cross-sectional view of the pressure chamber assembly ofFIG. 8 in an open position;

FIG. 10 is a cross-sectional view of an upper guard heater forming apart of the pressure chamber assembly of FIG. 8;

FIG. 11 is a top plan view of the upper guard heater of FIG. 10;

FIG. 12 is a bottom plan view of the guard heater of FIG. 10;

FIG. 13 is a cross-sectional view of a lower guard heater forming a partof the pressure chamber assembly of FIG. 8;

FIG. 14 is a bottom plan view of the lower guard heater of FIG. 13;

FIG. 15 is an enlarged, cross-sectional, fragmentary view of thepressure chamber assembly of FIG. 8;

FIG. 16 is a perspective view of a cup seal forming a part of thepressure chamber assembly of FIG. 8;

FIG. 17 is a fragmentary, perspective view of the cup seal of FIG. 16;

FIG. 18 is a cross-sectional view of a pressure chamber assemblyaccording to further embodiments of the present invention;

FIG. 19 is a cross-sectional view of a pressure chamber assemblyaccording to further embodiments of the present invention;

FIG. 20 is a top plan view of a chuck forming a part of the pressurechamber assembly of FIG. 19;

FIG. 21 is a bottom plan view of the chuck of FIG. 20;

FIG. 22 is a cross-sectional view of the chuck of FIG. 20 taken alongthe line 22—22 in FIG. 21;

FIG. 23 is a cross-sectional, schematic view of a pressure chamberassembly according to further embodiments of the present invention;

FIG. 24 is a top plan view of a chuck forming a part of the pressurechamber assembly of FIG. 23;

FIG. 25 is a cross-sectional view of the chuck of FIG. 24 taken alongthe line 25—25 of FIG. 24;

FIG. 26 is a cross-sectional view of a pressure chamber assemblyaccording to further embodiments of the present invention;

FIG. 27 is a bottom view of a spray member forming a part of thepressure chamber assembly of FIG. 26;

FIG. 28 is a cross-sectional view of the spray member of FIG. 27 takenalong the line 28—28 of FIG. 27; and

FIG. 29 is a bottom plan view of a spray member according to furtherembodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now is described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

The present invention relates generally to, inter alia, the cleaning ortreating of microelectronic substrates (such as semiconductorsubstrates) during or subsequent to the manufacturing of integratedcircuits, microelectronic devices, MEM's, MEOM's and opto-electronicdevices. Removal of surface contaminants and particulates is a key stepin the integrated circuit fabrication process. There are numerouscleaning steps (commonly referred to as “cleans”) in the fabricationprocess. The different types of cleans include pre-diffusion cleans,front end of the line post-ash cleans, back end of the line post-etchcleans, pre-metal deposition cleans, front end of the line plasma strip,back end of the line clean/strip, post-ion implantation cleans andpost-chemical mechanical planarization (CMP) cleans. There are manytypes and sources of particulates and contaminants in the fabricationprocess. The particles and contaminants may be molecular, ionic, atomicor gaseous in nature. The source may be inherent (e.g., redeposition ofresist) or extrinsic to the process (e.g., wafer transport).

The shift of interconnect systems shift from Al/SiO₂ to Cu/low-kpresents new challenges that may be effectively addressed using themethods and apparatus of the present invention. For example, a primaryproblem with the transition to Cu is the tendency of Cu to corrode whenexposed to an oxidizing environment, because Cu does not have theself-passivating properties of Al. Corrosion of Cu during cleans of dualdamascene structures can result in high contact resistance, undercuttingand lift-off of the dielectric layers, thereby reducing circuit yields.Additional concerns have focused on the chemical compatibility oftraditional cleans with low-k materials. As an example, it has beendemonstrated that amine chemistries gas from OSG and other inorganicspin-on dielectric films, causes via poisoning. Aspects of the presentinvention may address the currently challenging cleans of these newinterconnect systems.

With reference to FIG. 1, an apparatus 10 according to preferredembodiments of the present invention is shown therein. As illustrated,the apparatus 10 is adapted to clean a surface of a wafer substrate 5.However, it will be appreciated by those of skill in the art from thedescription herein that various features and aspects of the apparatusand the methods described hereinbelow may be used for cleaning orotherwise treating wafers or other types of substrates or workpieces.Additionally, it will be appreciated by those of skill in the art fromthe description herein that various components and steps as describedherein below may be omitted or replaced with other (for example,conventional) components or steps as appropriate.

The wafer 5 may be, for example, a wafer of semiconductor material suchas silicon, silicon oxide, gallium arsenide, etc. The wafer 5 has asubstantially planar work surface 5A and an opposing substantiallyplanar backside surface 5B. A continuous or discontinuous layer of wastematerial is disposed on the work surface 5A. The waste layer may be alayer of photoresist, reactive ion etch residue, chemical mechanicalpolishing residue or post-ion implantation residue. The waste materialin the aforementioned layers may include inorganic or organiccontaminants such as polymers based on stryenic, acrylic, novolac,cyclic olefinic maleic anhydride resins; etch residue based on ions offluorine, chlorine, bromine or iodine; and slurry residue containingsilica or alumina abrasives with other common slurry additives such asoxidizers, buffers, stabilizers, surfactants, passivating agents,complexing agents, corrosion inhibitors or other agents. Other types ofworkpieces may be cleaned or otherwise treated using the apparatusincluding, for example, MEMS, MEOMS, opto-electronic devices, and 3-Dmicro/nano-structures.

The apparatus 10 includes generally a flow/pressure control system 100,a recirculation system 200, a supply/recovery system 300, a pressurechamber assembly 400, and a substrate handling system 500 (FIG. 8). Thepressure chamber assembly 400 includes a pressure chamber 410. Asdiscussed in greater detail below, the wafer 5 is held in the pressurechamber 410 for processing. The flow/pressure control system 100conditions and applies a chemistry or chemistries (also referred to asadjuncts or modifiers), CO₂ (in the form of liquid, gas, and/orsupercritical fluid (ScCO₂)), and/or a mixture of chemistries and CO₂ tothe working surface 5A of the wafer 5. The substrate handling system 500holds the wafer 5 and, optionally, moves the wafer 5 to facilitateuniform cleaning. The recirculation system 200 may be used to filter andreturn process fluid to the pressure chamber 410. The supply/recoverysystem 300 supplies the process fluids and may be employed to cleanpost-process effluent and, optionally, return a portion thereof(typically, recovered CO₂) for further use in the apparatus 10.

Turning to the flow/pressure control system 100 in greater detail, thesystem 100 includes a tank T1 containing CO₂ at high pressure. Thepressure of the CO₂ in the tank T1 is preferably between about 400 psiand 4000 psi, depending on the process(es) to be executed using theapparatus 10. The volume of the tank T1 is preferably at least 5 timesthe volume of the pressure chamber 410. A temperature control device maybe operatively connected to the tank T1. The temperature control devicemay be, for example, a temperature sensor and a heating coil or probe orheat exchanger. The temperature of the CO₂ in the tank T1 is preferablybetween about 0° C. and 90° C., depending on the processes to beexecuted using the apparatus 10. The CO₂ may be in liquid, gas orsupercritical phase.

A plurality of outlet lines L3, L4 and L5 are fluidly connected to thetank T1. In the event that it may be desired to supply liquid CO₂ fromthe tank T1, the lines L3, L4 and L5 preferably draw from a lowerportion of the tank T1 (e.g., via a lower outlet or a dip tube). Theoutlet lines L3, L4 and L5 fluidly connect the tank T1 to a chemistrysupply/conditioning system 120 (schematically illustrated in FIG. 1 anddescribed in greater detail below), a feed line L1, and a feed line L2.Valves V1, V2 and V3 are provided to control flow in the lines L3, L4and L5, respectively.

A plurality of chemistry supplies S1, S2, S3 are fluidly connected tothe system 120. Each supply S1, S2, S3 may include a single chemistry ormultiple compatible chemistries that are combined at or upstream of therespective supply S1, S2, S3. The supplies may include the respectivechemistries disposed in suitable containers. Where feasible, thecontainers are preferably at atmospheric pressure to allow forconvenient refilling.

The chemistries provided by the supplies S1, S2, S3 may include, forexample: water; oxidizers such as peroxides or permanganates; acids suchas hydrofluoric, sulfuric, and nitric; bases such as secondary andtertiary amines; ammonium hydroxide; solvents such as organiccarbonates, lactones, ketones, ethers, alcohols, sulfoxides, thiols, andalkanes; surfactants such as block copolymers or random copolymerscomposed of fluorinated segments and hydrophilic or lipophilic segments;surfactants with siloxane-based components and hydrophilic or lipophiliccomponents; conventional ionic and non-ionic hydrocarbon-basedsurfactants; and salts such as ammonium fluoride and choline.Incompatible chemistries are chemistries which, when combined or exposedto one another, tend to react with one another in a manner that impedesthe process and/or damages or unduly fouls the apparatus 10 or wafer 5.Examples of incompatible chemistries include acids and bases.

Level sensors may be provided in each of the supplies S1, S2, S3 toindicate that a refill is needed and/or to provide a metric of chemistryuse in the process. Means such as a heating coil or jacket may beprovided to control the temperatures of the supplies. A mixing devicemay be provided in each supply S1, S2, S3.

As discussed in more detail below, the system 120 is operable to provideone or more controlled volumes of chemistry (with or without CO₂), whichvolumes may be conditioned by the system 120. The feed lines L1 and L2are each fluidly connected to the system 120 to receive the volume orvolumes of the chemistries. The feed line L1 is fluidly connected to anozzle 191 in fluid communication with the pressure chamber 410. Thefeed line L2 is fluidly connected to a spray member 190 in the pressurechamber 410. Filters F1 and F2 are provided in the feed lines L1 and L2,respectively. Preferably and as illustrated, the filters F1, F2 arelocated downstream of all lines that feed into the feed lines L1, L2.

A vacuum line L16 is fluidly connected to the pressure chamber 410. Avacuum unit P1 is operable to draw a full or partial vacuum in thepressure chamber 410 through the line L16. The vacuum unit P1 may be apump or one or more tanks that are maintained at or near vacuum at alltimes by a continuously operating vacuum pump. A vacuum tank may beadvantageous in that the pressure chamber 410 may be evacuated morerapidly and the tank may be re-evacuated while wafer processing isoccurring. If multiple vacuum tanks are used, they may be staged intheir operation to generate greater vacuum in the pressure chamber 410in less time.

The vacuum unit P1 may be advantageous for managing the air (or ambientgas) introduced to the system. In each batch step, the pressure chamber410 may be opened and closed to insert and/or remove a substrate. Duringthe time when the pressure chamber 410 is open, the chamber may fillwith ambient gas (typically, air). Active control and management usingthe vacuum unit P1 may be used to prevent this insertion of ambient gasfrom building up over time in the process fluids (assuming some level ofrecycling of the process fluids is accomplished).

A circulation line L6 fluidly connects the pressure chamber 410 and thesystem 120. Preferably, the line L6 draws from a lower portion of thepressure chamber 410.

A secondary gas supply tank T2 is fluidly connected to the pressurechamber 410 with a controllable valve V15 provided therebetween.Preferably, the secondary gas has a higher saturated vapor pressure thanCO₂. Preferably, the secondary gas is an inert gas. More preferably, thesecondary gas is helium, nitrogen or argon.

Pulsing Feature

A variable volume device or pulse generator 102 may be fluidly connectedto the pressure chamber 410. The pulse generator 102 includes a chamber102B and a pressurizing member 102A movable in the chamber 102B. Thepulse generator 102 is operable to generate a rapid decrease and/orincrease (i.e., pulse) in pressure in the pressure chamber 410.Preferably, the swept volume of the pressurizing member 102A is betweenabout 0.1 and 5 times the volume of the pressure chamber 410.Preferably, the pulse generator 102 is adapted to provide pressurepulsing cycles at a rate of between about 1 cycle/10 seconds and 50cycles/second. Preferably, the pulse generator 102 is adapted todecrease and/or increase the pressure in the pressure chamber 410 by atleast 100 psi, and more preferably by between about 300 psi and 1500psi.

The pulse mechanism may be any suitable mechanism including, forexample, a piston coupled to a linear actuator, a rotating shaft and aconnecting rod, a magnetic piston movable by means of an externalelectric coil, and/or an electrically, pneumatically or hydraulicallydriven piston or diaphragm. In a hydraulic or pneumatic system, thepulse mechanism may be paired with valving to quickly admit and releasepressure to the non-process side of the diaphragm thereby displacing thepiston or diaphragm. In one embodiment, the high pressure tank T1 and alow pressure vessel such as T2 may be fluidly connected to providemotive force for the pulse mechanism (piston or diaphragm).

Suitable valving (not shown) may be added such that the pulse chamber102B is filled from one pathway, a valve in this pathway may be closedand the fluid may thereafter be driven back to the pressure chamber 410through a second pathway including a filter. The second pathway may feedthe returning fluid to the pressure chamber 410 through the spray member190. The multiple pathways may serve to prevent the reintroduction ofcontaminants just removed from the wafer or particles generated in thepulse chamber, if a piston is used.

While the pulse generator 102 is illustrated as connected to a bottomportion the pressure chamber 410, the pulse generator 102 may draw fromany height of the pressure chamber 410. In particular, it may bedesirable to configure the pulse generator 102 to draw from an upperportion when used to facilitate processes utilizing two-phase(liquid/gas) process fluids in the pressure chamber 410 or to affectfluid and particulate flow in the vicinity of the wafer. It may beadvantageous to move fluid rapidly away from the substrate surface(vertically), rather than move it across (parallel to) the wafer'ssurface as a bottom nozzle would. A relatively large pulse chamber maybe used to enable particle dislodgement from the wafer surface and alsoenable particle transport well away from the wafer, to preventredeposition. A relatively large pulse chamber may also be used toenable phase changes through two phases—such as from supercritical toliquid to gas.

An outlet line L10 and a valve V6 are provided to selectively vent thepressure chamber 410 to a lower pressure region, such as to a lowpressure tank T2 as discussed below, a fluid transfer device (e.g., apump), or atmosphere. Waste effluent from the pressure chamber 410 maybe drawn off to the low pressure region.

In addition to allowing removal of waste from the pressure chamber 410,the line L10 and the valve V6 may be used in tandem with thehigh-pressure tank T1 to generate pressure pulses in the pressurechamber 410. This may be accomplished by raising the pressure in thepressure chamber 410 using the tank T1 (i.e., by controlling one or moreof the valves V1, V2, V3 and/or other valves to provide an open pathbetween the tank T1 and the pressure chamber 410), closing the valve V6,and then rapidly dropping the pressure in the pressure chamber 410 byopening the valve V6. The waste effluent may go to a low pressure tank,for example, such as the tank T2. This sequence may be repeated asneeded.

Chemistry Supply/Conditioning System

The chemistry supply/conditioning system 120 is operable to provide aselected flow or amount of chemical adjuncts from the supplies S1, S2,S3 (more or fewer supplies may be used) to the pressure chamber 410.Moreover, the system 120 may be operable to selectively control thepressure, temperatures and flow rates of chemistries or chemistry/CO₂.In accordance with the present invention, certain alternativeconfigurations may be employed for the system 120 as describedhereinbelow. It will be appreciated from the description herein thatvarious aspects and features of the disclosed embodiments may be omittedor combined with or substituted for other aspects and features of theembodiments.

With reference to FIG. 2, a chemistry supply/conditioning system 120A isschematically illustrated along with certain relevant portions of theapparatus 10. A fluid transfer device P3 selectively draws or permitsgravity flow of chemistry fluid (“first flow”) from the supply S1 to areservoir R1 at substantially ambient pressure. A level measuring device122 measures the volume of the fluid in the reservoir and thereby thevolume of the chemistry to be delivered to the pressure chamber 410. Thefluid transfer device P3 may also serve to determine the volume of thefluid in the reservoir R1 by metering the flow through the device P3.The chemical adjunct in the reservoir may thereafter drain under forceof gravity through a conditioning unit C1 (as discussed below), thefilter F1, and the line L1 into the pressure chamber 410.

Alternatively, CO₂ (e.g., supercritical CO₂ (ScCO₂), liquid CO₂, orcompressed liquid CO₂ or gaseous CO₂) from the tank T1 may be deliveredto the reservoir R1 through a line L3A by operation of a valve V1A. Apressurized mixture of the adjunct and CO₂ is thereby delivered to thepressure chamber 410 through the unit C1, the filter F1, and the lineL1.

With further reference to FIG. 2, the system 120A is adapted to delivera second flow of chemistry-containing process fluid to the pressurechamber 410, the second flow including chemistry from the supply S2which is not compatible with the supply S1. The system 120A provides aflow path for the second flow that is separate from that used for thefirst flow. The second flow path includes elements P4, R2, 122, and C2corresponding generally to elements P3, R1, 122, and C1.

In the same manner as discussed above, the second flow may be achemistry only stream (i.e., no CO₂) that is transferred to reservoir R2via P4 and then through the conditioning unit C2, the filter F2, and theline L2 to the pressure chamber 410. Alternatively, CO₂ from the tank T1may be introduced into the reservoir R2 through a line L3B by operationof a valve V1B such that the adjunct/CO₂ is delivered to the pressurechamber 410 under pressure.

FIG. 2 further illustrates the use of the circulation line L6 to returnprocess fluid from the pressure chamber 410 to the reservoir R2 by usingP4 or a pressure differential. The returned fluid may be remixed withthe second flow for reuse in the process. A further filter (not shown)may be provided in the line L6.

With reference to FIG. 3, a chemistry supply/conditioning system 120Baccording to further embodiments of the present invention is showntherein. The system 120B is particularly well-suited for deliveringgaseous chemistries. The system 120B corresponds to the system 120Aexcept that the reservoirs R1, R2 are omitted and high pressure CO₂ ismade directly available to the conditioning units C1, C2 via lines L3A,L3B and valves V1A and V1B. By operation of the fluid transfer device P3(or P4), the system 120B may inject the adjunct S1 (or S2) through theconditioning unit C1 (or C2) and the filter F1 (or F2) and into thepressure chamber 410. Alternatively, high pressure CO₂ may be added toand mixed with the chemistry S1 or S2 in the respective conditioningunit C1, C2. In this case, the volume of the chemistry delivered to thepressure chamber 410 may be measured by metering the flow of thechemistry through the fluid transfer device P3 (or P4) or by measuringthe volume change in the supply vessels S1 or S2. The flow rate(s) ofchemistries and/or CO₂ to the conditioning units C1 and C2 may also becontrolled to achieve a desired ratio of CO₂ to chemistry in the streambeing delivered to chamber 410.

With reference to FIG. 4, a chemistry supply/conditioning system 120Caccording to further embodiments of the present invention is showntherein. The system 120C includes a fluid transfer device P5 operable toselectively draw alternatingly from each of the supplies S1 and S2 aswell as the supply of high pressure CO₂ from the tank T1 (via line L3Aand valve VIA). The device P5 forces the selected chemistry through aconditioning unit C3 and one or both of the filters F1 and F2 (dependingon the operation of valves V9 and V10) so that the fluid is ultimatelyinjected into the pressure chamber 410 under pressure. Optionally, CO₂from the tank T1 may be added to the selected chemistry by introducingthe CO₂ into the conditioning unit C3 using the line L3B and the valveV1B. In order to prevent mixing of the incompatible chemistries S1, S2,CO₂ (preferably, pure ScCO₂) from the tank T1 is introduced through theline L3A to flush the fluid transfer device P5 and the remainder of theflow path to the pressure chamber 410 shared by the two chemistry flows.

Recirculation System

The recirculation system 200 includes an outlet line L7 fluidlyconnected to a lower portion of the pressure chamber 410. Lines L8 andL9 are in turn fluidly connected to the line L7 and also to the feedlines L1 and L2, respectively, upstream of the filters F1 and F2. Afluid transfer device P2 is operable to draw fluid from the pressurechamber 410 and force the fluid through the lines L8 and L9 andultimately back into the pressure chamber 410. The recirculated fluidflow may be combined with other fluid flow in the lines L1 and L2 (e.g.,from the system 120 and/or from the lines L3 or L4). Valves V4 and V5are provided in the lines L8 and L9.

The recirculation system 200 may serve to provide additional fluidmechanical action to the wafer surface without requiring additionalremoval of CO₂ and/or chemistry and introduction of new CO₂ and/orchemistry. Moreover, the recirculation system 200 may serve tocontinuously clean (e.g., filter, distill, or separate componentsthrough density modulation) the process fluid during the cleaningprocess.

An alternative recirculation system 200A according to the presentinvention is shown in FIG. 5. The system 200A includes an outlet lineL14. Return lines L15 and L16 fluidly connect the line L14 to arecirculation nozzle 193 and the spray member 190, respectively, in thepressure chamber 410. A fluid transfer device P6 is operable to forcefluid from the pressure chamber 410 through a filter F3 and back intothe pressure chamber 410 through the nozzle 193 and/or the spray member190. Valves V7 and V8 are provided to enable alternating delivery offluid to the spray member or recirculation nozzle and to preventunintended back flow through the nozzle 193.

A further alternative recirculation system 200B according to the presentinvention is shown in FIG. 6. The system 200B includes an outlet lineL30 fluidly connecting the pressure chamber 410 to a still 243 (having aheating element 245) through a transfer system 242. The transfer system242 converts the waste stream from the pressure chamber 410 from itsstarting state (e.g., liquid, compressed liquid, or supercritical fluid)to a liquid. Preferably, the transfer system 242 is also adapted toprevent backflow of fluids from the still 243 to the pressure chamber410. For this purpose, the transfer system 242 may include one or moreshut-off valves and/or one-way/check valves.

If the waste stream from the pressure chamber 410 is a liquid, thetransfer system 242 may not change the fluid or may merely change thetemperature of the fluid (e.g., using a heater or chiller). If the wastestream from the pressure chamber 410 is a compressed liquid, thetransfer system may provide a pressure let down (e.g., by means of atorturous path, an orifice, or control valve). The transfer system 242may also include a temperature-altering element. If the waste streamfrom the pressure chamber 410 is a supercritical fluid, there ispreferably a pressure let-down as discussed above as well as atemperature-altering step. In this case, it may be necessary ordesirable to cool the fluid to cross into the 2-phase Liquid/Gas regionof the phase diagram.

Once in the liquid state, the fluid is boiled/distilled in the still 243to separate the fluid into two components: a lighter component, whichwill be predominantly CO₂ gas, and a heavier component which will bepredominantly adjunct chemistry and entrained contaminants. The heaviercomponent may be conveyed (e.g., by gravity) to a recycling/disposalsystem 244.

The CO₂ gas (lighter) stream is directed to a heat exchanger 246 via aline L31 where the CO₂ gas stream is converted (through manipulation oftemperature and pressure) to the conditions of the processing fluid(i.e., liquid, compressed liquid or supercritical fluid). If the fluidstarting condition was liquid, the exchanger may include a heat transfercoil 247 connected to the heating device so as to transfer heat from thecondensing fluid to the still 243. The CO₂ may be additionally cleanedthrough filtration, adsorption, absorption, membrane separation,physical separation (e.g., centrifugal force) or electrostaticseparation. The conditioned CO₂ may then be provided back toadditionally process the substrate or to process a subsequent substrate.Additional chemistries may be added to this incoming fluid (e.g., at amixing reservoir 248).

The distilling recirculation system 200B may be used to provide acontinuous or intermittent flow of the process fluid through thepressure chamber 410. The mass flow may serve to assist in the cleaningprocess by transporting particulates away from the wafer 5 (e.g., toprevent redeposit on the wafer) and/or providing mechanical action(agitation) on the wafer surface. The mass flow may be filtered orotherwise conditioned. The mass flow may be fully driven by the additionof heat in the still 243 so that no pumps or other potentiallyparticulate-generating mechanical devices are required. Multipletransfer systems 242, stills 243, heat exchangers 246 may be used toprovide increased continuous flow.

Each of the recirculation systems 200, 200A, 200B may be employed toprovide mass flow through the chamber 410 without loss of process fluidmass from the process loop (except the relatively small quantities ofadjuncts and particulates that are filtered or distilled out of theprocess fluid stream. Moreover, each of the recirculation systems 200,200A may be employed to provide mass flow through the chamber 410without altering the chemical composition of the process fluid.

As depicted in FIGS. 1-5, the filters F1, F2 as well as the filter F3are preferably adapted to provide filtration of at least particles inthe range of 10 nm (as in nanometers) to 50 microns. Suitable filtersmay include sintered filters, bag-type filters, magnetic filters,electrostatic filters, and/or combinations thereof. Preferably, as inthe illustrated embodiments, every fluid stream pathway into thepressure chamber 410 has a filter as its final element before thepressure chamber 410. In particular, all valves and fluid transferdevices for delivering fluid to the pressure chamber 410 are disposedupstream of at least one filter.

The conditioning units C1, C2, C3 may include means for mixing thechemistries of the adjunct or for mixing the adjunct and CO₂ (whenpresent) to promote homogeneity and solvation of adjuncts. Theconditioning units may also include means for controlling thetemperature of the adjunct or adjunct/CO₂. Suitable mixing devices orprocesses include mechanical mixers and flow mixing. Temperature controlmay be achieved using probes, internal coils, elements, and/or anexternal jacket, for example. An electrical heater or a fluid heatexchanger may be used, for example.

The fluid transfer devices P3, P4, P5 are preferably capable ofaccurately and consistently metering a flow of fluid. Suitable devicesmay include diaphragm pumps, syringe pumps, or piston pumps, forexample.

While particular arrangements have been illustrated and describedherein, it will be apparent to those of skill in the art that variousmodifications may be made in keeping with the present invention. Forexample, in the system 120A (FIG. 2), the circulation line L6 may feedto the fluid transfer device P3 such that the flow from the line L6 isdirected to the line L1. Valving (not shown) may be provided to allowselection of the feed line (i.e., L1 or L2) for each flow path, so thatthe chemistry (with or without CO₂) from the supply S1, for example, canbe directed to either or both of the spray member 190 and the nozzle191, as desired. The apparatus 10 may include one or more chemistrysupply paths that include an in-line reservoir (i.e., as in the system120A) and/or one or more parallel chemistry supply paths that are directinjection (i.e., as in the system 120B) and/or one or more parallelchemistry supply paths that serve alternative supplies (i.e., as in thesystem 120C). Additional filters, fluid transfer devices, reservoirs,conditioning units and valving may be provided as needed to provideadditional flexibility.

Cleaning/Pulsing Process

The apparatus 10 may be used to execute a wide range of processeswherein the wafer 5 in the pressure chamber 410 is subjected to fluidstreams, pools and atmospheres, including chemical adjuncts, CO₂ andmixtures thereof, in various states (e.g., liquid, gas, supercriticalfluid). Such processes may serve to clean or otherwise treat (e.g.,coat) the wafer surface 5A. For example, the apparatus 10 may be used toconduct methods as disclosed in the following commonly owned U.S. patentapplications, the disclosures of which are hereby incorporated herein byreference in their entireties:

1. U.S. patent application Ser. No. 09/951,259; inventors James P.DeYoung, James B. McClain, Michael E. Cole, and David E. Brainard; filedSep. 13, 2001; and titled Methods for Cleaning MicroelectronicStructures with Cyclical Phase Modulation (Attorney Docket No.5697-45IP);

2. U.S. patent application Ser. No. 09/951,249; inventors James P.DeYoung, James B. McClain, Stephen M. Gross, and Joseph M. DeSimone;filed Sep. 13, 2001; and titled Methods for Cleaning MicroelectronicStructures with Aqueous Carbon Dioxide Systems (Attorney Docket No.5697-45IP2);

3. U.S. patent application Ser. No. 09/951,092; inventors James P.DeYoung, James B. McClain, and Stephen M. Gross; filed Sep. 13, 2001;and titled Methods for Removing Particles from MicroelectronicStructures (Attorney Docket No. 45IP3);

4. U.S. patent application Ser. No. 09/951,247; inventor(s) James P.DeYoung, James B. McClain, and Stephen M. Gross; filed Sep. 13, 2001;and titled Methods for the Control of Contaminants Following CarbonDioxide Cleaning of Microelectronic Structures (Attorney Docket No.5697-45IP4).

The following are exemplary processes that may be practiced inaccordance with the present invention. Preferably, the valving, fluidtransfer devices, and sensors are operatively connected to acomputerized controller to provide feedback and control as needed toconduct the desired process steps.

The wafer 5 is inserted into the pressure chamber 410 and secured to thechuck 510 by any suitable means such as adhesive or clamps. Morepreferably, the wafer 5 is secured to the chuck in one of the mannersdescribed below with regard to the wafer holding assemblies 520 (FIG.19) and 550 (FIG. 23). The door of the pressure chamber is thereafterclosed and sealed.

Air and any other gases in the pressure chamber 410 are evacuated fromthe pressure chamber 410 through the line L16 using the vacuum unit P1.

Optionally, chemistry from one or more of the supplies S1, S2, S3 may beapplied to the wafer using the chemistry supply/conditioning system 120prior to pressurizing the pressure chamber 410.

The pressure chamber 410 is thereafter pressurized with CO₂ (preferablyliquid CO₂ or ScCO₂) from the high-pressure tank T1. Preferably, thepressure chamber 410 is pressurized to a pressure of at least 400 psi,and more preferably, between about 800 psi and 3000 psi. Additionally,the atmosphere in the pressure chamber 410 is maintained at a selectedtemperature (preferably between about 10° C. and 80° C.), for example,using a guard heater as discussed below.

Once the pressure chamber 410 is pressurized to the selected pressure,dense-phase CO₂ is circulated through the line L2 to the spray member190 and/or the nozzle 191. The spray member directs the dense-phase CO₂onto the wafer surface 5A. Optionally, chemistry, with or without liquidor supercritical CO₂ mixed therewith, from one or more of the suppliesS1, S2, S3 may be applied to the wafer using the chemistrysupply/conditioning system 120.

The pulse generator 102 and/or the high-pressure tank T1 and the valveV6 are then used to effectuate cyclical phase modulation (CPM). Moreparticularly, the pulse generator 102 and/or the high-pressure tank T1and the valve V6 are operated (with appropriate temperature control ofthe process fluid) to effect phase changes between liquid,supercritical, and gas states. Preferably, the phase changes areeffected between supercritical and liquid states in a cyclical fashion.For example, CPM processes as disclosed in the commonly owned U.S.patent application Ser. No. 09/951,259; inventors James P. DeYoung,James B. McClain, Michael E. Cole, and David E. Brainard; filed Sep. 13,2001; and titled Methods for Cleaning Microelectronic Structures withCyclical Phase Modulation (Attorney Docket No. 5697-45IP), thedisclosure of which is hereby incorporated herein by reference in itsentirety, may be conducted.

During the CPM cycles, CO₂ or CO₂ with chemistry may be applied to thewafer 5 via the spray member 190. Fluid and particulate matter from thepressure chamber 410 may be removed from the pressure chamber 410 andrecirculated locally via the recirculation system 200 or 200A and/orrecirculated via the line L6 and the system 120.

The process fluid (dense-phase CO₂, adjuncts and waste matter) isremoved from the pressure chamber 410 via the line L10. As discussedbelow, CO₂ may be withdrawn from the pressure chamber 410 to a recoverytank. The process pathways (including the pressure chamber 410) may beflushed one or more times with pure liquid or supercritical CO₂ from thetank T1.

The foregoing steps of optionally applying one or more of thechemistries S1, S2, S3 to the wafer (with or without ScCO₂), conductingCPM and removing the process fluid may be repeated as needed. Followingthe final CPM cycle, the process fluid is removed and optionally arinsing fluid (e.g., a co-solvent or surfactant) is dispensed from thesupplies S1, S2, S3 onto the wafer 5 (preferably under pressure from thespray member 190).

The pressure chamber 410 and the process pathways (including therecirculation pathway) are thereafter flushed with ScCO₂ from the tankT1 to remove adjuncts and remaining residues. If no rinse fluid is used,a pure CO₂ (liquid or supercritical) fluid is used to remove adjunctsand remaining contaminants from the substrate. The flushing dense-phaseCO₂ may be recirculated, but is finally removed via the line L10. Afinal rinse of the wafer 5 and the pressure chamber 410 is preferablyconducted using pure liquid or supercritical CO₂.

Thereafter, the pressure chamber 410 is depressurized and the wafer 5 isremoved.

Preferably, the apparatus 10 is operable to apply the process fluid fromthe spray member 190 onto the wafer surface at a pressure of at least400 psi, and more preferably between about 800 psi and 3000 psi. Theprocess may include applying the process fluid to wafer using the spraymember 190 with the spray member 190 rotating relative to the wafer.Either or both the spray member (e.g., the spray member 190 or the spraymember 602) and the chuck (e.g., the chuck 510, 522, or 552) may berotationally driven.

Moreover, a flow of process fluid may be provided across the wafer 5 byfeeding the process fluid into the chamber 410 via a feed nozzle (e.g.,the nozzle 191) and simultaneously removing process fluid through one ormore of the outlet lines (e.g., the line L7, the line L10, the line L11,and/or the line L6). Preferably, the apparatus 10 is operable to providesuch a flow through the chamber 410 at a rate of at least 2 gpm.

As noted above, the process may include simultaneously pulsing thedensity of the CO₂ containing process fluid and spraying the processfluid onto the wafer 5. Likewise, if the phase modulation isaccomplished using the pulse generator 102, a flow of the process fluidthrough the chamber 410 may be provided at the same time as the densitymodulation. The wafer 5 and/or the spray member 190 may besimultaneously rotated.

In each of the foregoing steps involving the application of chemistries,the chemistries may be any suitable chemistries. In particular, it iscontemplated that the chemistries may include co-solvents, surfactants,reactants, chelants, and combinations thereof. Notably, the separateflow paths and/or flushing means of the chemistry supply system 120 maybe used to safely and effectively add incompatible chemistries to thechamber 410.

The apparatus may deliver process components in different states (e.g.,liquid, gas, supercritical) to the chamber 410 and may allow forcomponents in different states to coexist in the chamber 410. Theapparatus may provide heated CO₂ gas (e.g., from the tank T1) to drainor flush process components from the cleaning chamber for cleaning stepsusing liquid CO₂. Alternatively, the apparatus may deliver a secondarygas such as helium, nitrogen or argon from the secondary gas tank T3 todisplace process fluids during a cleaning step and preceding a rinsestep when either liquid or supercritical CO₂ is used as the primaryprocess fluid during the cleaning step. The apparatus may also provideheated ScCO₂ (e.g., supercritical CO₂) at a temperature higher than thatof the primary processing fluid but at a density lower than that of theprimary processing fluids used to displace processing fluids after acleaning step, but prior to a rinse step for cleaning steps using ScCO₂.

Supply/Recovery System

The supply/recovery system 300 is adapted to supply and/or recycle andre-supply CO₂ and/or chemistry to the cleaning process. As the processproceeds, some CO₂ will be lost. The process may include batch cycleswhere the pressure chamber 410 is pressurized and depressurized manytimes in succession as the substrates (e.g., wafers are moved throughthe CO₂-based processing equipment). For example, some CO₂ will be lostto atmosphere when the pressure chamber is opened to remove and replacewafers. Some CO₂ will be lost from the system in the waste stream thatis drained from the system. Substantial amounts of the CO₂ will becontaminated or otherwise rendered unsuitable or potentially unsuitablefor further recirculation through the process loop. For these reasons,it is necessary to provide sources of additional CO₂ to replenish theCO₂ lost from the process. Additionally, it may be desirable to recycleCO₂ as well as chemistry for reuse in the apparatus 10 or elsewhere.

Stock CO2 Supply

With reference to FIG. 7, the supply/recovery system 300 includes a CO₂stock supply 312. The supply 312 may be, for example, CO₂ supplied inone or more liquid cylinders, carboys of sub-ambient liquid, or bulksupply systems of sub-ambient liquid. The storage method preferablyallows for supply of either liquid or gaseous CO₂.

The supply 312 is fluidly connected to the process chamber 410 via aline L17, which is provided with a valve V11 to control the flow intothe pressure chamber 410. Preferably, the system 300 is adapted suchthat the CO₂ from the supply can be delivered directly (i.e., withoutaid of any fluid transfers devices, pressurizing tanks, or the like)into the pressure chamber 410 at a desired pressure (preferably betweenabout 15 and 50 psig). The supply 312 may be from a gas or liquidsource.

CO₂ as commonly distributed for industrial and commercial uses (e.g.,food processing such as carbonation of beverages and freeze-drying, pHcontrol, or dry ice) is not sufficiently clean for processing ofmicro-electronic substrates. Commonly, such CO₂ supplies includecontaminants such as organic materials, other gases, water andparticulate matter. Accordingly, the system 300 may include apurification unit D1 between the supply 312 and the pressure chamber410. The purification unit D1 is operative to purify the CO₂ supply tothe requisite ultra-high cleanliness and purity. In this manner, thepurification unit D1 enables the effective use of food grade orindustrial grade CO₂, thereby allowing the use of existing supply chainsand distribution chains for CO₂.

The purification unit D1 may include one or more of the following meansfor filtering gas or liquid CO₂:

1. Distillation: The CO₂ may be drawn from a gaseous supply or a gaseousportion of the supply. Liquid CO₂ may be drawn, boiled, relocated to acollection volume and re-condensed;

2. Filtration;

3. Membrane separation (preferably paired with distillation); and

4. Absorption/adsorption (e.g., capture based on attractive forces ormolecule size).

CO₂ may also be delivered to the process (and, more particularly, to thepressure chamber 410) by introducing additional CO₂ into the vapor-saverunit 320 discussed below. Preferably, this additional CO₂ is firstpurified using a purification unit corresponding to the purificationunit D1.

Waste Stream Handling

As noted above in the discussion regarding the process, at various times(including, typically, at the end of each run), processing fluid may beremoved from the pressure chamber 410 via the line L10. Such fluids mayinclude liquid, gaseous, or supercritical CO₂, chemistry, and variouscontaminants (e.g., particles dislodged from the wafer(s)).

The system 300 includes a low-pressure tank T2 to receive the wastestream drawn removed from the pressure chamber 410. The tank T2 ispreferably maintained at a pressure of between about ambient and 3000psi. The volume of the tank T2 is preferably at least 5 times the volumeof the pressure chamber 410.

Different compositions may be expelled to the tank T2, in which case thetank T2 is a segmented tank or multiple tanks. The pressure in the tankT2 is less than that of a pressure head upstream of and fluidlycommunicating with the pressure chamber 410 so that the pressuredifferential forces the waste stream into the tank T2 from the pressurechamber 410. Preferably, the high-pressure tank T1 provides the pressurehead so that no pump or other mechanical device is required.

The reduction in pressure of the CO₂ as it is transferred from thepressure chamber 410 to the tank T2 may be used to facilitateseparation. Supercritical CO₂ process fluid may be expanded through apressure reduction device (e.g., a control valve or orifice) to a lowerpressure. At this lower pressure, components of the processing fluid(e.g., chemical adjuncts or entrained contaminants) may be renderedinsoluble, thereby facilitating the efficient separation of the expandedstream into a light-fluid CO₂ stream and a heavy-fluid (insoluble)alternate stream.

A supercritical CO₂ process fluid may also be expanded through apressure reduction to the two-phase Liquid/Gas area of the phasediagram. This may enable the segmentation of different process fluids indifferent segmented volumes of a divided tank or multiple tanks. Suchsegmentation may be advantageous to could mitigate the generation ofmixed waste streams, which may be more costly to manage than singlecomponent fluid streams. Segmentation may also enable the utilization ofdistillation for separation of the processing fluid components (e.g.,separation of CO₂ for recycle from chemical adjuncts and entrainedcontaminants for disposal).

A liquid process fluid stream may be expanded and heated to thegas-state. This would allow a continuous distillation-like separation ofcomponents (i.e., evaporation of flash evaporation), for example, asdescribed below with regard the distillation system 340.

Recycling and Abatement

The waste stream received in the tank T2 is thereafter transferred to arecycling/abatement station 310 through a line L29 (which is providedwith a valve V12). The waste stream may be transferred by means of apump or the like, but is preferably transferred using a non-mechanicalmeans such as pressure differential and/or gravity. To the extent thewaste stream has been separated in the tank T2, there may be two of moreseparate lines delivering the respective separated streams for separatehandling by the unit 310. These streams may be treated and directed bythe system 300 in the following manners:

1. CO₂ may be disposed of through controlled venting or draining via aline L27 to a safe atmospheric discharge and/or collection for unrelateduse;

2. CO₂ may be directly supplied to the pressure chamber 410 via a lineL22. The CO₂ is preferably purified by means of a purification unit D3.The CO₂ as delivered to the pressure chamber 410 through the line L22may be at greater than atmospheric pressure, in which case it may beused to perform or augment the pressurization of the main processingchamber at the beginning of each cycle;

3. CO₂ may be directed to the purification unit D1 through the line L23and thereafter into the pressure chamber 410;

4. Gaseous CO₂ may be directed through a purification unit D2, through aliquefying unit 314 (which adjusts the pressure and chills the CO₂ gas),and supplied to the stock CO₂ supply 312 for further use in the mannerdescribed above;

5. CO₂ may be passed through a purification unit D4 and re-pressurizedand supplied to the high-pressure tank T1 through a line L25 using apressurizing device (e.g., a pump) P8;

6. CO₂ may be directed via a line L26 through a purification unit D5 toa vapor saver tank 320 as discussed below; and

7. Chemical adjuncts and contaminants may be treated and/or disposedof/recycled through a line L28 and in accordance with good chemicalstewardship.

Vapor Recovery

Following draining of the process fluid from the pressure chamber 410, apressurized CO₂ vapor will remain in the pressure chamber 410. It isdesirable and often necessary to remove this vapor prior to opening thepressure chamber 410 to remove the substrate(s) (e.g., wafer(s)).

One method for depressurizing the chamber is to vent the chamber using acontrolled release. Alternatively, a compressor or pump may be used todraw down the pressure in the pressure chamber 410.

The pressure of the CO₂ may also be reduced using a vapor recoverysystem 322 and method as follows. Such methods and apparatus may employfeatures and aspects of the methods and apparatus disclosed in U.S.patent application Ser. No. 09/404,957, filed Sep. 24, 1999 and in U.S.patent application Ser. No. 09/669,154, filed Sep. 25, 2000.

A vapor recovery tank or pressurized container 322 is used to rapidlycapture CO₂ (typically, gas or SCF) at the end of a process cyclethrough a line L18. The captured CO₂ is typically a gas or supercriticalfluid, but may be a liquid (in which case, the venting is preferablyfrom the bottom of the chamber 410 to avoid formation of solid/dry ice).In this manner, the pressure chamber 410 may be depressurized veryrapidly. Advantageously, the capturing method is not constrained by thevolumetric throughput of a mechanical device (e.g., a compressor). Thevolume of the vapor recovery tank 322 is preferably on the order of oneto 500 times the volume of the pressure chamber 410.

The captured CO₂ may be handled in any desired manner, including:

a) it may be disposed of through a line L21 having a valve V10, andpreferably through a surge tank 324;

b) using the line L21 and surge tank 324, it may be recovered andrecycled for use in another application (e.g., a CO₂-based firesuppression system or a storage container for recycle for use in someother service);

c) it may be recovered and recycled for use in the same application(compressed and/or liquified, and/or converted into SCF) and re-suppliedto the processing system or to the CO₂-supply system;

d) it may be used in the next processing step to pressurize the pressurechamber 410 (which may be a prerequisite for pressurizing the pressurechamber 410 up to sufficient pressure to effectively add CO₂ basedprocessing fluids).

The vapor recovery system may include a compressor P7 for assisting thetransfer of material from the pressure chamber 410 to the vapor recoverytank(s). For example, at the end of a processing cycle, the pressurechamber 410 may be at high pressure (CO₂-gas at vapor pressure or asupercritical fluid, 300<P (psia)<3000) and the vapor recovery tank maybe at a low pressure. In order to depressurize the pressure chamber 410to a low (e.g., ambient) pressure very quickly (e.g., to allow openingof the chamber and removal of the substrate) while saving the majorityof the CO₂, the two chambers may be equalized, and then:

a) a compressor may be used to push more CO₂ from the main processingchamber to the vapor-saver tank; and

b) a second vapor recovery tank may be used (e.g., in cascading manner)to again rapidly equilibrate and additionally lower the pressure of thepressure chamber 410.

A compressor may also be used to remove the material from the vaporrecovery tank(s) between the end of a first run and the end of the nextrun at which time the vapor recovery tank(s) may be required to be atlow pressure again. The captured CO₂ may be handled in any of themanners described above.

It will be appreciated that various valving and flow control apparatusin addition to that illustrated may be employed in the system 300. Thevapor-saver system 320 and the several options for handling the CO₂ fromthe waste stream of line L10 are independent and any may be eliminatedfrom the system 300 as desired. Each of the purification units D2, D3,D4, D5 may correspond to the purification unit D1 (i.e., may use any ofthe methods listed above—distillation, filtration, membrane separation,and absorption/adsorption). As an alternative to the severalpurification units D2, D3, D4, D5, two or more of these purificationunits may be combined so that the respective flow paths each have acommon extent through the shared purification unit and thereafterdiverge.

Pressure Chamber Assembly

With reference to FIGS. 8 and 9, the pressure chamber assembly 400includes an upper casing 420 and a lower casing 430. When in a closedposition as shown in FIG. 8, the casings 420, 430 define a pressurechamber 410 therebetween and a sealing system 450 as described in moredetail below seals the chamber 410. When in a closed position as shownin FIG. 8, a pair of opposed clamps 440 surround end portions of thecasings 420, 430 to limit separation of the casings 420, 430. The clamps440 can be displaced to allow the casings 420, 430 to be separated intoan open position as shown in FIG. 9.

Guard Heater

A guard heater assembly 460 is disposed in the chamber 410 and includesan upper guard heater 462 and a lower guard heater 472. The guard heaterassembly 460 defines a holding volume 411 between the heaters 462, 472.A platen or chuck 510 is disposed in the holding volume 411 between theguard heaters 462, 472 and is adapted to support the wafer 5 forrotation about a vertical axis between the guard heaters 462, 472. Aspray member 190 is mounted in a groove 464F the upper guard heater 462and adapted to direct fluid through nozzles 192 onto the working surface5A of the wafer.

The casings 420, 430 are preferably each unitarily formed of stainlesssteel or other suitable metal. Passages 422A, 422B, 422C are formedthrough the casing 420. Passages 432A, 432B, 432C are formed through thecasing 430. As best seen in FIG. 9, the casing 420 has an annular flange424 with an outer, annular recess 425 formed therein and defined in partby a vertical wall 425A. The casing 430 has an annular flange 434 withan annular groove 435 formed therein. The flange 434 has a vertical wall434A. The casings 420 and 430 have opposing annular abutment faces 426and 436, respectively.

With reference to FIGS. 10-12, the upper guard heater 462 includes aninterior member 464 having a top wall 464A and an annular side wall464B. A spiral flow channel 466A is formed in the top wall 464A. Anouter plate 467 covers the top wall 464A. An annular surrounding member468 surrounds the side wall 464B and defines an annular surroundingchannel 466B therewith. A channel 466C fluidly connects the channels466A and 466B. An inlet 466D in the top plate 467 fluidly connects thepassage 422A to the channel 466B, and an outlet 466E fluidly connectsthe passage 422B to the channel 466A. The outer plate 467 and the wall468 are secured to the interior member 464 by welds 8, for example. Thespray member 190 extends through an opening 467A in the outer plate 467and is retained (e.g., by an upstream nozzle or screws) in a groove 464Cin the top wall 464A. The nozzles 192 of the spray member 190 arefluidly connected to the passage 422C. The interior member 464, theouter plate 467 and the surrounding wall 468 are preferably formed ofstainless steel. The guard heater 462 may be secured to the casing 420by screws with small standoffs holding the screws off of the walls.

With reference to FIGS. 13 and 14, the lower guard heater 472 includesan interior member 478 and an outer plate 474 secured thereto by welds8, for example. An opening 479 extends through the outer plate 474, andan opening 476D extends through the interior member 478. A spiral flowchannel 476A is formed in the interior member 478. An inlet passage 476Bin the outer plate 474 fluidly connects the passage 432A to the channel476A, and an outlet passage 476C fluidly connects the passage 432B tothe flow channel 476A. The interior member 478 and the outer plate 474are preferably formed of stainless steel or other suitable metal. Theguard heater 472 may be secured to the casing 430 by screws with smallstandoffs holding the screws off of the walls.

Preferably, the guard heaters 462, 472 each have a surface area (i.e.,the “interior”, inwardly facing surfaces) to volume ratio of at least0.2 cm²/cm³. More preferably, the guard heaters 462, 472 each have asurface area to volume ratio of between about 0.2 and 5.0 cm^(2/)cm³,and most preferably of about 0.6 cm²/cm³.

As discussed above, the temperature of the wafer environment (i.e., thechamber 410 and the fluid(s) therein) is preferably controlled duringand between the cleaning and other process steps. The temperature in thechamber 410 is controlled using the guard heater assembly 460. Moreparticularly, a flow of temperature control fluid is introduced throughthe passage 422A, through the inlet opening 466D, through the channel466B, through the passage 466C, through the passage 466A, through theoutlet opening 466E and out through the passage 422B. In this manner,heat from the temperature control fluid is transferred to the guardheater 462 to heat the guard heater 462 (when the fluid is hotter thanthe guard heater 462) or, alternatively, heat from the guard heater 462is absorbed and removed by the fluid to cool the guard heater 462 (whenthe fluid is cooler than the guard heater 462). The lower guard heater472 may be heated or cooled in the same manner by a temperature controlfluid that flows through the passage 432A, through the inlet opening476B, through the channel 476A, through the outlet opening 476C, andthrough the passage 432B.

The temperature control fluids may be any suitable fluid, preferably aliquid. Suitable fluids include water, ethelyne glycol, propelyneglycol, mixtures of water with either ethelyne or propelyne glycol,Dowtherm A (diphenyl oxide and diphenyl), Dowtherm E,(0-dichlorobenzene), mineral oil, Mobiltherm (aromatic mineral oil),Therminol FR (chlorinated biphenyl). Most preferably, the temperaturecontrol fluids are a 50%/50% mixture of water and ethelyne glycol. Thefluid may be heated by any suitable means such as an electric, gas-firedor steam heater. The fluid may be cooled by any suitable means such asfluid chiller, for example, of vapor compression refrigeration type orevaporative type.

The guard heater assembly 460 and the casings 420, 430 are spaced apartto define an insulating gap 470 therebetween that substantiallyenvelopes the guard heaters 462, 472. More particularly, an insulatinggap 470A is defined between the outer plate 467 and the adjacentsurrounding wall portions of the casing 420 and preferably has a widthA. An insulating gap 470B is defined between the surrounding wall 468and the adjacent wall of the casing 420 and has a width B. An insulatinggap 470C is defined between the outer plate 474 and the adjacentsurrounding wall portion of the casing 430 and has a width C.Preferably, each of the widths A, B and C is at least 0.1 mm. Morepreferably, each of the widths A, B and C is between about 0.1 and 10mm, and most preferably about 1.0 mm.

The insulating gap 470 may serve to substantially increase theefficiency, controllability and manufacturing throughput of the system10. The insulating gap 470 may substantially thermally insulate theguard heaters 462, 472 from the casings 420, 430 so that the effect ofthe temperatures of the casings 420, 430 on the atmosphere surroundingthe wafer 5 is reduced or minimized. Restated, the insulation gap 470may substantially limit the thermal mass that must be heated or cooledby the temperature control fluids to the thermal masses of the guardheaters 462, 472. Accordingly, the temperature of the process fluid maybe controlled such that it is substantially different than that of thecasings 420, 430.

While a fluid flow heating/cooling arrangement is illustrated anddescribed above, other means for heating/cooling the guard heaters 462,472 may be employed in addition to or in place of fluid heating. Forexample, electrical resistance coils (e.g., designed to radiate heatdirectly to the wafer) may be provided in the guard heaters 462, 472.

With reference to FIG. 18, a pressure chamber assembly 400A according toalternative embodiments of the present invention is shown therein. Theassembly 400A differs from the assembly 400 only in that the guardheater assembly 460A thereof includes insulating layers 471, 473 inplace of the insulating gap 470. The guard heaters 462, 472 may besecured to the insulating layers 471, 473 which are in turn secured tothe casings 420, 430, respectively.

The insulating layers 471, 473 may be formed of crystallinefluoropolymers such as PCTFE (polychlorotrifluoroethylene), PTFE(polytetrafluoroethylene), or PVF2 (polyvinylidene difluoride).Preferably, the insulating layers 471, 473 are formed of bulk PTFE,virgin PTFE or glass-filled PTFE. The insulating layers 471, 473 may behoney-combed, open cellular, or otherwise constructed or configured toenhance the insulating performance thereof.

Preferably, the guard heater assemblies 460, 460A are adapted to providetemperatures in the pressure chamber 410 ranging from about 0° C. to 90°C. Preferably, the guard heater assemblies 460, 460A are adapted toprovide heat to the atmosphere in the pressure chamber 410 at a maximumrate of at least 500 joules/second.

Pressure Chamber Sealing System

The casings 420, 430 which define the pressure chamber 410 also define afluid leak path 3 (FIG. 15) at the interface from the pressure chamber410 to an exterior region 7 (e.g., the ambient atmosphere (directly orindirectly)). The sealing system 450 is adapted to restrict (fully orpartially) the flow of fluid along the fluid leak path 3.

As best seen in FIG. 15, the sealing system 450 includes an O-ring 452,an annular cup (or chevron) seal 454, an annular spring 456 and anannular retaining ring 458. As discussed below, the combination of theseals 452, 454 serves to improve the effectiveness and durability of thepressure chamber seal.

The retaining ring 458 is fixed to the flange 424 and extends radiallyoutwardly toward the flange 434 and below the recess 425. The retainingring 458 may be formed of stainless steel or other suitable material.The retaining ring 458 may be secured to the flange 424 by any suitablemeans, for example, threaded fasteners.

The cup seal 454 is shown in FIGS. 16 and 17. “Cup seal” as used hereinmeans any self-energized seal that has a concave portion and isconfigured such that, when the concave portion of the seal ispressurized (e.g., by a pressurized chamber on the concave side of theseal), the seal is thereby internally pressurized and caused to exert anoutward force (e.g., against adjacent surfaces of a pressure vesseldefining the pressure chamber), to thereby form a seal. The cup seal 454includes an annular inner wall 454B joined along an annular fold 454C toan annular outer wall 454A and defining an annular channel 454D therein.

The cup seal 454 is preferably unitarily formed of a flexible resilientmaterial. Preferably, the cup seal 454 is formed of a material that isresistant to swelling and damage when exposed to dense CO₂. Suitablematerials include fluorinated polymers and elastomers, such as PTFE(Teflon®, DuPont), filled PTFE, PTFE copolymers and analogs, such as FEP(fluorinated ethylene/propylene copolymers), Teflon AF, CTFE, otherhighly stable plastics, such as poly(ethylene), UHMWPE (ultra-highmolecular weight poly(ethylene)), PP, PVC, acrylic polymers, amidepolymers, and various elastomers, such as neoprene, Buna-N, andEpichlorohydrin-based elastomers. Suitable seal materials can beobtained from PSI Pressure Seals Inc., 310 Nutmeg Road South, SouthWindsor, Conn. 06074.

The cup seal 454 may be secured to the flange 424 by affixing at leastone, and preferably both, of the inner wall 454B and the fold 454C tothe adjacent portions of the flange 424 and/or the retaining ring 458.The inner wall 454B, 454C may be secured to the flange 424 usingadhesive, for example. Preferably, the cup seal 454 is retained by theretaining ring 458 without the use of adhesive or the like.

The spring 456 may be any suitable spring capable of repeatedly andreliably biasing the outer wall 454A away from the inner wall 454B(i.e., radially outwardly). Preferably, the spring 456 biases the cupseal 454 radially outwardly beyond the flange 424 when the casings 420,430 are separated (see FIG. 9). Preferably, the spring 456 is a woundwire spring or a cantilever type spring having a shape similar to, butsmaller than, the cup seal 454 and nested inside the cup seal 454. Thespring 456 is preferably formed of spring grade stainless steel. Thespring 456 may be integrally formed with the cup seal 454. In additionto or in place of the provision of the spring 456, the cup seal 454 maybe formed so as to have an inherent bias to spread the walls 454A, 454Bapart. Moreover, the spring 456 may be omitted and the cup seal 454 maybe provided with no inherent bias.

The O-ring 452 is disposed in the groove 435. Preferably, the O-ring 452is secured in the groove 435 by an interference fit. The O-ring isformed of a deformable, resilient material. Preferably, the O-ring 452is formed of an elastomeric material. More preferably, the O-ring 452 isformed of bunna-n or neoprene, and most preferably of EDPM. The O-ring452 is sized such that, when the O-ring 452 is in its unloaded state(i.e., when the casings 420, 430 are separated; see FIG. 9), a portionof the O-ring 452 will extend above the abutment face 436.

When the casings 420, 430 are closed, the cup seal 454 is capturedbetween the flanges 424 and 434 as shown in FIGS. 8 and 15. The spring456 biases the walls 454A and 454B against the walls 434A and 425A,respectively. When the chamber 410 is pressurized above the ambientpressure, the pressure exerted in the channel 454D forces the walls 454Aand 454B apart and into tighter, more sealing engagement with therespective walls 434A and 425A.

In this manner, the cup seal 454 provides a secure, primary seal thatprevents or substantially reduces the flow of the fluid from the chamber410 to the O-ring 452 along the fluid leak path 3. The O-ring 452 isthereby spared potentially damaging exposure to the process fluid. Suchprotection of the O-ring 452 may substantially extend the service lifeof the O-ring 452, particularly where the process fluid includes highpressure CO₂. Accordingly, the sealing system 450 may provide for a highthroughput wafer manufacturing system with relatively long-lived seals.

Notably, when the chamber 410 is pressurized, the casings 420, 430 maybe separated somewhat by the internal pressure so that the O-ring 452 isnot well-loaded for sealing. Because the cup seal 454 serves as aprimary seal, a secure sealing arrangement may nonetheless be provided.However, in the event of a partial or complete failure of the cup seal454, the O-ring 452 may serve to prevent or reduce leakage of theprocess fluid to the environment. According to certain embodiments, theassembly 400 may be adapted such that the O-ring 452 will allow fluid topass along the fluid leak path 3 when the chamber 410 is at at least aselected pressure so that the O-ring is not pressurized and no damagingprocess fluid (e.g., CO₂) is in contact with the O-ring for extendedperiods of time.

When the fluid in the chamber 410 is at atmospheric pressure or vacuum,the sealing effectiveness of the cup seal 454 will typically bediminished (however, the bias of the spring 456 may provide some sealingperformance). In this event, the O-ring 452 may serve as the primaryseal to prevent or reduce leakage of atmospheric fluid into the chamber410 through the fluid leak path 3. Notably, the atmospheric fluid(typically air) typically will not include high concentrations of CO₂ orother components unduly harmful to the O-ring material.

Preferably, and as illustrated, the O-ring 452 sealing arrangement is abutt-type arrangement so that no sliding components are present. Thepressure energizing mechanism of the cup seal 454 allows for use of arelatively low bias force for the spring 456. These aspects of theinvention assist in minimizing the generation of any particles that maybe detrimental to the wafer 5. The cup seal 454 may be otherwiseoriented or located in the pressure chamber assembly. Two or more of thecup seals 454 may be arranged in series along the fluid leak path.

From the description herein, it will be appreciated that the combinationof a cup seal and an elastomeric O-ring seal overcomes certain problemsassociated with high pressure sealing of CO₂ holding vessels thattypically neither an elastomeric O-ring seal nor a cup seal canovercome. In particular, elastomeric O-rings are generally notlong-lived when exposed to high-pressure CO₂ and then rapidlydepressurized. Cup seals when used as pressure seals typically require alarge pre-load spring to enable the same vessel for vacuum service. Suchlarge pre-load may cause greater friction and wear and, thus, generationof damaging/contaminating particles. In accordance with the presentinvention, the elastomeric O-ring may be externally energized(compressed) when required to establish a vacuum within the chamber.

Wafer Holding Assembly

With reference to FIGS. 19-22, a wafer holding assembly 520 according tofurther embodiments of the present invention is shown therein. Theassembly 520 may be used in place of the chuck 510 in a pressure chamberassembly 400B (FIG. 19) otherwise corresponding to the pressure chamberassembly 400. As will be better appreciated from the followingdescription, the wafer holding assembly 520 includes a substrate holderor platen or chuck 522 and is adapted to retain the wafer on the chuck522 by means of a pressure differential generated by rotation of thechuck 522.

The chuck 522 has a front surface 524 and an opposing rear surface 528.A plurality (as shown, eight) of impeller vanes 529 extend rearwardlyfrom the rear surface 528 and radially outwardly with respect to acentral rotation axis E—E (FIG. 19). A plurality (as shown, four) ofpassages 526A extend fully through the chuck 522 from the rear surface528 to a circumferential channel 526B formed in the front surface 524. Aplurality (as shown, sixteen) of channels 526C extend radially outwardlyfrom and fluidly communicate with the channel 526B. Additionalcircumferential channels (not shown) may fluidly connect the channels526C.

As shown in FIG. 19, the chuck 522 is mounted on a driven shaft 530 forrotation therewith about the rotational axis E—E. As the chuck 522 isrotated, the impeller vanes 529 tend to push or force the fluid betweenthe rear surface 528 and the adjacent, opposing surface 412 of thepressure chamber 410 radially outwardly in the directions F toward theouter periphery of the chuck 522. A pressure differential is therebygenerated beneath the chuck 522 between the inner region (i.e., nearestthe axis E—E) of the chuck 522 and the outer region of the chuck. Moreparticularly, the pressure in the central region (including the pressureat the lower openings of the passages 526A) is less than the pressure atthe outer edges of the chuck 522 and the pressure in the chamber 410 onthe side of the wafer 5 opposite the chuck 522. As a result, adifferential is created between the fluid pressure exerted on the topsurface of the wafer 5 and the pressure of the fluid in the channels526B, 526C.

In the foregoing manner, the wafer 5 is secured to the chuck 522 as thechuck 522 and the wafer 5 are rotated. In order to retain the wafer 5 onthe chuck 522 prior to initiating rotation or during process stepswithout rotation, and/or in order to provide additional securement,supplemental holding means may be provided. Such supplemental means mayinclude, for example, adhesive, clamps, and/or an externally generatedpressure differential assembly such as the wafer holding assembly 550described below.

With reference to FIGS. 23-25, a wafer holding system 551 according tofurther embodiments of the present invention is shown therein. Thesystem 551 includes a wafer holding assembly 550 and may be used inplace of the chuck 510 in a pressure chamber assembly 400C (FIG. 23)otherwise corresponding to the pressure chamber assembly 400 (forclarity, certain elements of the assembly 400C are not shown). Theassembly 400C is further provided with a magnetic drive assembly 580.

As will be better appreciated from the following description, the waferholding assembly 550 includes a substrate holder or platen or chuck 552and is adapted to retain the wafer 5 on the chuck 552 by means of apressure differential between the pressure in the pressure chamber 410and the pressure at an outlet 564. The magnetic drive system 580 isadapted to drive the chuck 552 relative to the pressure chamber 410without requiring sealing directly between relatively moving elements(namely, a shaft 560 and the casing 430). It will be appreciated thatthe wafer holding system 551 may be used with other drive arrangementsand that the magnetic drive assembly 580 may be used with other waferholder mechanisms.

Turning to the magnetic drive assembly 580 in greater detail, theassembly 580 includes an upper housing 585 and a lower housing 584. Theupper end of the upper housing 585 is received in the casing 430 suchthat a gas-tight seal is provided therebetween (e.g., by means of asuitable sealing device such as a gasket). The shaft 560 extends throughthe housing 585 and is rotatably mounted thereon by upper and lowerbearings 586 and 588. A seal 561 is positioned between the shaft 560 andthe housing member 585. The seal 561 is preferably a non-contact seal.More preferably, the seal 561 is a gap seal (more preferably, defining agap G having a width of between about 0.001 and 0.002 inch) or alabyrinth seal. The seal 561 may also be a lip seal or a mechanicalseal.

An internal magnet holder 590 is mounted on the lower end of the shaft560 for rotation therewith and has an inner magnet M1 mounted on anouter portion thereof. The internal magnet carrier 590 is disposed inthe lower housing member 584. A pressure cap 596 surrounds the internalmagnet carrier 590 and forms a gas-tight seal (e.g., by means of asuitable sealing device such as a gasket) with the lower end of thelower housing member 584. In this manner, the pressure cap 596 and theupper housing member 585 together form a gas-tight reservoir for fluidsthat may enter the upper housing member 585 from the pressure chamber410.

A drive unit 582 is mounted on the housing member 584. The drive unit582 may be any suitable drive device such as a hydraulically driven unitor, more preferably, an electrically driven unit. The drive unit 582 isoperable to rotate a shaft 594 that extends into the housing member 584.An external magnet holder 592 is mounted on the shaft 594 for rotationtherewith. The external magnet holder 592 is disposed in the housingmember 584, but is mechanically and fluidly separated from the internalmagnet holder 590 and the pressure chamber 410 by the pressure cap 596.An external magnet M2 is mounted on the external magnet holder 592 forrotation therewith.

The magnets M1 and M2 are relatively constructed, arranged andconfigured to such that they are magnetically coupled to one another. Inthis manner, the magnets M1, M2 serve to indirectly mechanically couplethe external magnet holder 592 and the internal magnet holder 590, andthereby the shaft 594 and the shaft 560. Thus, the chuck 522 may berotated by operation of the drive unit 582.

The magnetic drive assembly 580 may be any suitable drive assembly withsuitable modifications as described herein. Suitable magnetic driveassemblies include the BMD 150, available from Büchi AG of Uster,Switzerland. Moreover, other types of non-mechanically coupling driveunits may be used.

As best seen in FIGS. 24 and 25, the chuck 552 has a front surface 554.A countersunk passage 556B extends fully through the chuck 552. Aplurality of channels 526A extend radially outwardly from and fluidlycommunicate with the passage 556B. Additional circumferential channels(not shown) may fluidly connect the channels 526A.

As shown in FIG. 23, the chuck 552 is mounted on the driven shaft 560 bya nut 558 for rotation with the shaft 560 about a rotational axis F—F.The shaft 560 has an axially extending connecting passage 562 extendingtherethrough. The nut 558 has a central aperture that allows fluidcommunication between the passage 562 and the passage 556B. A passage563 extends radially through the shaft 560 and fluidly connects thepassage 562 to the secondary chamber 565 defined between the housing 585and the shaft 560. Preferably, the seal 561 is a non-contact seal (e.g.,a gap seal or a labyrinth seal) forming a restricted flow passage thatprovides fluid communication between the pressure chamber 410 and thesecondary chamber 565.

An outlet 564 in the housing member 585 fluidly connects the secondarychamber 565 with a line L40. A line L41 having a valve V30 fluidlyconnects a flow restrictor 566 and a storage tank 568 to the line L40.The flow restrictor 566 may be a throttling orifice or a suitablepartial closure valve such as a needle valve adapted to provide acontrolled limit on flow therethrough. A line L42 having a valve V31fluidly connects a fluid transfer device P20 (e.g., a vacuum pump) tothe line L40.

The system 551 may be used in the following manner to secure the wafer 5to the chuck 552. A pressure is provided in the storage tank 568 that isless than the pressure of the atmosphere in the pressure chamber 410under typical process conditions. During processing, the valve V30 isopened so that the secondary chamber 565 is placed in fluidcommunication with the storage tank 568 which serves as a passive lowpressure source (i.e., no pump, compressor or the like is employed togenerate the pressure or vacuum). In this manner, the pressure in thechamber 565 (and, therefore, in the fluidly communicating channels 556A)is less than the pressure in the pressure chamber 410. A pressuredifferential is thereby generated between the upper surface of the wafer5 and the backside of the wafer 5, causing the wafer 5 to be drawn downonto the chuck 552 in the direction D.

The flow restrictor 566 serves to limit flow of fluid from the secondarychamber 565 to the storage tank 568, thereby providing a controlledleak. The controlled leak serves to ensure a that sufficientdifferential pressure is provided across the wafer 5 to hold it in placewithout allowing undue loss of the fluid from the pressure chamber 410.

Preferably, the pressure of the storage tank 568 is greater thanatmospheric pressure, but less than the pressure of the pressure chamber410 during the intended processes. The storage tank 568 may permit gasthat is drawn from the pressure chamber 410 to be cleaned and recycledor otherwise disposed of.

Alternatively, the storage tank 568 may be omitted or bypassed such thatthe line L41 vents directly to atmosphere when the valve V30 is opened.

If the pressure of the atmosphere in the pressure chamber 410 is thesame as or less than the pressure of the passive low pressure source(i.e., the storage tank 568 or the ambient atmosphere), the fluidtransfer device P20 may be operated to reduce the pressure in thechamber 565 to less than the pressure in the pressure chamber 410 togenerate the desired amount of pressure differential across the wafer 5.In this event, the valve V30 is closed and the valve V31 is opened.

Preferably, the system 551 is operable to generate a pressure in thechannels 556A that is at least 1 psi less than the pressure in thepressure chamber 410, and more preferably, between about 5 and 20 psiless.

Rotating Spray Member

The spray member 190 as described above as well as the spray members602, 652 described below provide dispersed inlets to deliver processfluids directly to the surface of the wafer. Moreover, the spray membersprovide a distributed stream of these fluids that incorporatesmechanical action from the fluid/surface impingement. This mechanicalaction is generally the result of the momentum of the fluid streamcoming out of the spray member.

Design of the spray member (including, for example, number, spacing andsizes of spray ports) may be used to selectively control the use of theenergy transfer/mechanical action. Additionally, simultaneous rotationof the wafer may serve to generate shear (momentum) between the fluidand the wafer surface to further facilitate removal of materials fromthe surface.

With reference to FIG. 26, a pressure chamber assembly 400D according tofurther embodiments of the present invention is shown therein. Theassembly 400D may be the same as the assembly 400 (certain aspects notshown in FIG. 26 for clarity), for example, except for the provision ofa rotating spray member assembly 600. The assembly 400D may include arotatively driven wafer holder 510 or the wafer 5 may be heldstationary. The spray member assembly 600 may be used with any of theabove-described pressure chamber assemblies. Notably, the spray memberassembly 600 may be used to provide relative rotation between a spraymember and a wafer without requiring a rotating wafer holder.

The spray member assembly 600 includes a spray member 602 as also shownin FIGS. 27 and 28. The spray member 602 includes a shaft portion 610and bar-shaped distribution portion 620. An axial passage 612 extendsfrom an upper opening 614 and through the portion 610 and fluidlycommunicates with a lateral passage 622 in the portion 620. A series ofspray ports 624 extend from the passage 622 to the lower, outer edge ofthe distribution portion 620. The spray member 602 may be formed of ahighly oxidatively stable material such as 316 stainless steel.

A bearing 630 is fixed within a passage 427 in the casing 420 such thata flange 632 of the bearing 630 is received in an enlarged portion 427Aof the passage 427. The bearing 630 is preferably a sleeve bearing asshown. The bearing 630 may be formed of PTFE, PE or PEEK. Preferably,the bearing 630 is formed of PTFE.

The shaft portion 612 extends through the bearing 630 and has a flange616 overlying the flange 632. An end cap 640 is securely mounted to thecasing 420 in the portion 427A and over the flange 616, for example, bythreading. Preferably, the end cap 640 forms a gas pressure tight sealwith the casing 420.

The end cap 640 is adapted to receive a supply of process fluid (e.g.,from a supply line 9) such that the flow of process fluid is directedthrough a passage 642 and into the passage 612. The fluid continues intothe passage 622 and is dispensed through the ports 624.

With reference to FIGS. 27 and 28, the ports 624A are angled withrespect to the intended rotational axis N—N (see FIG. 28) of the spraymember 602. Preferably, the ports 624 are disposed at an angle M (FIG.28) of between about 0 and 85 degrees, and more preferably of betweenabout 30 and 60 degrees. The ports 624 are angled opposite the directionR (FIG. 27) of intended rotation.

In use, the reaction force responsive the fluid exiting the ports 624(i.e., the hydraulic propulsion) causes the spray member 602 to rotateabout the axis N—N within the bearing 630. Notably, because the bearing630 is mounted internally (i.e., within the high pressure region) of thepressure chamber 410 separated from ambient pressure by the end cap 640,the bearing is not subjected to loading from a substantial pressure dropthereacross.

Alternatively or in addition to the hydraulically driven rotation, thespray member 602 may be coupled to a drive unit. The spray member may bedirectly or indirectly mechanically coupled to the drive unit (e.g.,using a bearing/seal/drive unit configuration) or may benon-mechanically coupled (e.g., using a coupling force forelectromagnetic or magnetic (permanent, electro- or induction-driven)coupling). Some or all of the ports 624 may be oriented parallel to theaxis of rotation N—N.

A spray member 652 according to further embodiments of the presentinvention may be used in place of the spray member 602 and with any ofthe foregoing modifications or features. The spray member 652 has ashaft portion 660 and corresponds to the spray member 602 except thatthe bar-shaped distribution portion 620 is replaced with a plate- ordisk-shaped distribution portion 670 having a pattern of spray ports 674formed therein. The pattern of the spray ports 674 may be modified.

It will be appreciated that various of the inventions describedhereinabove and as reflected in the claims that follow may be used forprocesses other than those specifically discussed above with regard tothe preferred embodiments. For example, the means and methods forholding a wafer to a chuck may be employed to hold other types ofsubstrates, in other types of processes (e.g., processes not involvingCO₂ or wafer fabrication). The supply/recovery system 300 and thesubsystems thereof may be used in other systems and processes using CO₂containing process fluids, such as chemical mechanical planarization(CMP) systems employing CO₂.

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention. Therefore,it is to be understood that the foregoing is illustrative of the presentinvention and is not to be construed as limited to the specificembodiments disclosed, and that modifications to the disclosedembodiments, as well as other embodiments, are intended to be includedwithin the scope of the invention.

That which is claimed is:
 1. A method for holding a substrate to asubstrate holder in a pressure chamber, the method comprising the stepsof: a) providing a first pressure in the pressure chamber; b) providinga substrate holder assembly including: 1) a substrate holder disposed inthe pressure chamber, the substrate holder including a front surfaceadapted to support the substrate; 2) a housing defining a secondarychamber; 3) at least one connecting passage providing fluidcommunication between the front surface of the substrate holder and thesecondary chamber; and 4) a drive shaft connected to the substrateholder, wherein the drive shaft is rotatable relative to the housing; c)mounting the substrate on the substrate holder such that the substratecovers the connecting passage; and d) providing a second pressure in thesecondary chamber that is lower than the first pressure using a passivelow pressure source such that the passive low pressure source draws thesubstrate toward the front surface of the substrate holder.
 2. Themethod of claim 1 including providing a controlled leak of fluid fromthe secondary chamber to the passive low pressure source.
 3. The methodof claim 1 wherein the substrate holder assembly includes a restrictivepassage providing fluid communication between the pressure chamber andthe secondary chamber.
 4. The method of claim 1 wherein the step ofproviding a second pressure includes placing the secondary chamber influid communication with a volume at at least ambient pressure.
 5. Themethod of claim 1 wherein the step of providing a second pressureincludes placing the secondary chamber in fluid communication with astorage tank.
 6. The method of claim 1 further including the step ofoperating a vacuum pump in fluid communication with the secondarychamber.
 7. The method of claim 1 further including rotating thesubstrate holder and the substrate relative to the pressure chamber. 8.The method of claim 7 further including rotating the substrate holderand the substrate relative to the housing.
 9. The method of claim 1wherein the housing and the secondary chamber surround at least aportion of the drive shaft.
 10. The method of claim 1 wherein thehousing is fixed relative to the vessel.
 11. The method of claim 1wherein the connecting passage includes a first passage portionextending axially through the drive shaft and a second passage portionextending radially through the drive shaft and fluidly connecting thefirst passage portion to the secondary chamber.
 12. A pressure chamberassembly for use with a substrate having a rear side, the pressurechamber assembly comprising: a) a vessel defining a pressure chamber; b)a substrate holder assembly including: 1) a substrate holder disposed inthe pressure chamber, the substrate holder including a front surfaceadapted to support the substrate; 2) a housing defining a secondarychamber; and 3) at least one connecting passage adapted to be covered bythe substrate when the substrate is mounted on the front surface of thesubstrate holder, the connecting passage providing fluid communicationbetween the rear side of the substrate and the secondary chamber whenthe substrate is mounted on the front surface of the substrate holdersuch that the substrate covers the connecting passage; c) a passive lowpressure source fluidly connected to the secondary chamber and therebyto the connecting passage to draw the substrate toward the front surfaceof the substrate holder; and d) a drive shaft connected to the substrateholder, wherein the drive shaft is rotatable relative to the housing.13. The pressure chamber assembly of claim 12 including a flowrestrictor adapted to allow a controlled leakage of fluid from thesecondary chamber to the passive low pressure source.
 14. The pressurechamber assembly of claim 13 wherein the flow restrictor includes arestrictive orifice.
 15. The pressure chamber assembly of claim 13wherein the flow restrictor includes a needle valve.
 16. The pressurechamber assembly of claim 12 wherein the substrate holder assemblyfurther includes a restrictive passage providing fluid communicationbetween the pressure chamber and the secondary chamber.
 17. The pressurechamber assembly of claim 16 including: a drive shaft connected to thesubstrate holder; and a seal member interposed between the drive shaftand the vessel; wherein the restrictive passage is defined between thedrive shaft and the seal member.
 18. The pressure chamber assembly ofclaim 17 wherein the seal member is a non-contact seal.
 19. The pressurechamber assembly of claim 12 wherein the passive low pressure source isan outlet to a volume at at least ambient pressure.
 20. The pressurechamber assembly of claim 19 wherein the passive low pressure source isan outlet to ambient air.
 21. The pressure chamber assembly of claim 19wherein the passive low pressure source is an outlet to a storage tank.22. The pressure chamber assembly of claim 12 including a supplementallow pressure source fluidly connected to the secondary chamber andthereby to the connecting passage to draw the substrate toward the frontsurface of the substrate holder.
 23. The pressure chamber assembly ofclaim 22 wherein the supplemental low pressure source includes a vacuumpump.
 24. The pressure chamber assembly of claim 12 including a valvebetween the secondary chamber and the passive low pressure source. 25.The pressure chamber assembly of claim 12 including at least one channelformed in the front surface of the substrate holder and in fluidcommunication with the connecting passage.
 26. The pressure chamberassembly of claim 12 including a drive shaft connected to the substrateholder, wherein the connecting passage extends through the drive shaft.27. The pressure chamber assembly of claim 12 wherein the housing andthe secondary chamber surround at least a portion of the drive shaft.28. The pressure chamber assembly of claim 12 wherein the housing isfixed relative to the vessel.
 29. The pressure chamber assembly of claim12 wherein the connecting passage includes a first passage portionextending axially through the drive shaft and a second passage portionextending radially through the drive shaft and fluidly connecting thefirst passage portion to the secondary chamber.
 30. A pressure chamberassembly for use with a substrate having a rear side, the pressurechamber assembly comprising: a) a vessel defining a pressure chamber; b)a substrate holder assembly including: 1) a substrate holder disposed inthe pressure chamber, the substrate holder including a front surfaceadapted to support the substrate; 2) a housing defining a secondarychamber; and 3) at least one connecting passage adapted to be covered bythe substrate when the substrate is mounted on the front surface of thesubstrate holder, the connecting passage providing fluid communicationbetween the rear side of the substrate and the secondary chamber whenthe substrate is mounted on the front surface of the substrate holdersuch that the substrate covers the connecting passage; c) a passive lowpressure source fluidly connected to the secondary chamber and therebyto the connecting passage to draw the substrate toward the front surfaceof the substrate holder; and d) a supplemental low pressure sourcefluidly connected to the secondary chamber and thereby to the connectingpassage to draw the substrate toward the front surface of the substrateholder.
 31. The pressure chamber assembly of claim 30 wherein thesupplemental low pressure source includes a vacuum pump.
 32. A methodfor holding a substrate to a substrate holder in a pressure chamber, themethod comprising the steps of: a) providing a first pressure in thepressure chamber; b) providing a substrate holder assembly including: 1)a substrate holder disposed in the pressure chamber, the substrateholder including a front surface adapted to support the substrate; 2) ahousing defining a secondary chamber; 3) a restrictive passage providingfluid communication between the pressure chamber and the secondarychamber; and 4) at least one connecting passage providing fluidcommunication between the front surface of the substrate holder and thesecondary chamber; c) mounting the substrate on the substrate holdersuch that the substrate covers the connecting passage; and d) providinga second pressure in the secondary chamber that is lower than the firstpressure such that a pressure differential between the first and secondpressures draws the substrate toward the front surface of the substrateholder.
 33. The method of claim 32 wherein the substrate holder assemblyincludes: a drive shaft connected to the substrate holder; and a sealmember interposed between the drive shaft and the vessel; wherein therestrictive passage is defined between the drive shaft and the sealmember.
 34. The method of claim 32 wherein the seal member is anon-contact seal.
 35. The method of claim 32 wherein the substrateholder assembly includes a drive shaft connected to the substrate holderand the drive shaft is rotatable relative to the housing.
 36. The methodof claim 35 wherein the housing and the secondary chamber surround atleast a portion of the drive shaft.
 37. The method of claim 35 whereinthe housing is fixed relative to the vessel.
 38. The method of claim 35wherein the connecting passage includes a first passage portionextending axially through the drive shaft and a second passage portionextending radially through the drive shaft and fluidly connecting thefirst passage portion to the secondary chamber.
 39. A pressure chamberassembly for use with a substrate having a rear side, the pressurechamber assembly comprising: a) a vessel defining a pressure chamber; b)a substrate holder assembly including: 1) a substrate holder disposed inthe pressure chamber, the substrate holder including a front surfaceadapted to support the substrate; 2) a housing defining a secondarychamber; 3) a restrictive passage providing fluid communication betweenthe pressure chamber and the secondary chamber; and 4) at least oneconnecting passage adapted to be covered by the substrate when thesubstrate is mounted on the front surface of the substrate holder, theconnecting passage providing fluid communication between the rear sideof the substrate and the secondary chamber when the substrate is mountedon the front surface of the substrate holder such that the substratecovers the connecting passage; and c) a low pressure source fluidlyconnected to the secondary chamber and thereby to the connecting passageto draw the substrate toward the front surface of the substrate holder.40. The pressure chamber assembly of claim 39 including: a drive shaftconnected to the substrate holder; and a seal member interposed betweenthe drive shaft and the vessel; wherein the restrictive passage isdefined between the drive shaft and the seal member.
 41. The pressurechamber assembly of claim 40 wherein the seal member is a non-contactseal.
 42. The pressure chamber assembly of claim 39 further including adrive shaft connected to the substrate holder, wherein the drive shaftis rotatable relative to the housing. 43.The pressure chamber assemblyof claim 42 wherein the housing and the secondary chamber surround atleast a portion of the drive shaft.
 44. The pressure chamber assembly ofclaim 42 wherein the housing is fixed relative to the vessel.
 45. Thepressure chamber assembly of claim 42 wherein the connecting passageincludes a first passage portion extending axially through the driveshaft and a second passage portion extending radially through the driveshaft and fluidly connecting the first passage portion to the secondarychamber.